Rename js snippets

snippets/js/s/mapped-array-symmetric-difference.md

@@ -0,0 +1,31 @@
+---
+title: Mapped array symmetric difference
+type: snippet
+language: javascript
+tags: [array]
+cover: dim-mountains
+dateModified: 2020-10-22T20:24:30+03:00
+---
+
+Returns the symmetric difference between two arrays, after applying the provided function to each array element of both.
+
+- Create a `Set` from each array to get the unique values of each one after applying `fn` to them.
+- Use `Array.prototype.filter()` on each of them to only keep values not contained in the other.
+
+```js
+const symmetricDifferenceBy = (a, b, fn) => {
+  const sA = new Set(a.map(v => fn(v))),
+    sB = new Set(b.map(v => fn(v)));
+  return [...a.filter(x => !sB.has(fn(x))), ...b.filter(x => !sA.has(fn(x)))];
+};
+```
+
+```js
+symmetricDifferenceBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [ 1.2, 3.4 ]
+symmetricDifferenceBy(
+  [{ id: 1 }, { id: 2 }, { id: 3 }],
+  [{ id: 1 }, { id: 2 }, { id: 4 }],
+  i => i.id
+);
+// [{ id: 3 }, { id: 4 }]
+```